Onesimus endeared himself to Paul by his piety and sincerity, no less than by his tender care for the apostle's comfort, and his zeal in promoting the work of the gospel. Paul saw in him traits of character that would render him a useful helper in missionary labor, and he counseled him to return without delay to Philemon, beg his forgiveness, and plan for the future. The apostle promised to hold himself responsible for the sum of which Philemon had been robbed. Being about to dispatch Tychicus with letters to various churches in Asia Minor, he sent Onesimus with him. It was a severe test for this servant thus to deliver himself up to the master he had wronged; but he had been truly converted, and he did not turn aside from his duty.

Paulus kom til at holde meget af Onesimus på grund af hans fromhed og oprigtighed og ikke mindst på grund af hans kærlige omsorg og hans iver for at fremme arbejdet for evangeliet. Paulus fandt karaktertræk hos ham, som kunne gøre ham til en nyttig hjælp i missionsarbejdet og han rådede ham til uden tøven at vende tilbage til Filemon, bede om hans tilgivelse og lægge planer for fremtiden. Apostlen lovede selv at stå inde for den sum, som var blevet berøvet Filemon. Da han netop skulle til at sende Tykikus af sted med breve til forskellige menigheder i Lilleasien, lod han Onesimus rejse sammen med ham. Det var en hård prøve for denne tjener således at udlevere sig til den herre, han havde besveget, men han var blevet virkelig omvendt og han veg ikke fra at gøre sin pligt.